This invention relates to a base film for a pressure-sensitive adhesive tape and a pressure-sensitive adhesive tape or sheet with the use of this base film as the substrate. This pressure-sensitive adhesive tape or sheet undergoes little dimensional change even under heating or with the passage of time. Particularly favorable effects can be achieved by using a pressure-sensitive adhesive tape or sheet wherein a polyolefin resin is used as the base film and a rubber pressure-sensitive adhesive containing a large amount of a tackifier resin is used as the pressure-sensitive adhesive.
Pressure-sensitive adhesive tapes have been widely employed in, for example, packaging, bonding, surface-protecting, masking, labeling and indicating in various industrial fields. In general, a pressure-sensitive adhesive tape comprises a pressure-sensitive adhesive for achieving the aimed performance and a base film for protecting and reinforcing the pressure-sensitive adhesive and imparting a smooth surface thereto.
Examples of known pressure-sensitive adhesives include rubber pressure-sensitive adhesives containing two components (namely, so-called a polymer elastomer and a tackifier) which are obtained by blending a rubber elastomer (for example, natural rubber, polyisoprene, polyisobutylene, butyl rubber, styrene/butadiene rubber) employed as the main component with a tackifier resin; acrylic pressure-sensitive adhesives made of polyacrylate optionally copolymerized with vinyl monomers (for example, vinyl acetate, methacrylates, acrylic acid, methacrylic acid); vinyl pressure-sensitive adhesives obtained by adding a plasticizer to a vinyl polymer (for example, vinyl chloride/vinyl acetate copolymer, polyvinyl acetate); and silicone pressure-sensitive adhesives containing rubbery siloxane and resin siloxane.
With respect to base materials for pressure-sensitive adhesive tapes, on the other hand, adequate ones are selected depending on, for example, the purpose of use from among various ones such as papers (for example, Japanese paper, kraft paper), fabrics (for example, cotton, stable fibers, synthetic fibers, non-woven fabric), plastics (for example, cellophane, polyethylene, polyester, polyvinyl chloride, acetate, polypropylene, polyethylene terephthalate, polystyrene, polyacrylonitrile) and metal foils.
It is frequently observed that these pressure-sensitive adhesive tapes, which are wound into rolls in many cases, undergo deformation such as gapping upon heating or with the passage of time. When pressure-sensitive adhesive tapes for indication or surface-protection are adhered to adherends, the base materials sometimes swell and thus cause lifting upon heating or with the passage of time.
These phenomena, which are caused by dimensional changes of the base materials, are particularly remarkable in pressure-sensitive adhesive tapes where a polyolefin resin is used as a base film and a rubber adhesive in which a large amount of a tackifier resin is compounded is used as an adhesive.
To overcome these problems encountering in the related art, the inventors have conducted intensive studies. As a result, they have found that a pressure-sensitive adhesive tape having a base film to which a tackifier resin has been preliminarily added undergoes little dimensional change even under heating or with the passage of time, thereby completing the invention.
Accordingly, the invention relates to a base film for a pressure-sensitive adhesive tape; and a pressure-sensitive adhesive tape or sheet which has a film having at least one layer of the base film as described above as the substrate and a pressure-sensitive adhesive layer formed on at least one face of the substrate.
Although it has not been clarified so far how these effects can be achieved, it is assumed that the tackifier resin might be prevented from migration from the pressure-sensitive adhesive layer toward the base material layer. Particularly remarkable effects can be achieved in pressure-sensitive adhesive tapes wherein a polyolefin resin is used as the base film and a rubber pressure-sensitive adhesive containing a large amount of a tackifier resin is used as the pressure-sensitive adhesive. This is seemingly because the tackifier resin can easily migrate owing to the high compatibility of the tackifier resin with the polyolefin resin.
The pressure-sensitive adhesive tapes of the invention are characterized by showing not only little dimensional change but little change in pressure-sensitive adhesive force.